Best motor for a mini treadmill?

[Imozeb]

Hi.

I need to build a mini treadmill for my project and I had a few questions which I hope you guys could answer. The treadmill needs to run at a maximum speed of 0.4 km/hr for around 3-4 hours. I also need to be able to control the speed somehow? The weight of the object on the treadmill is going to be less than a pound (It is a lizard treadmill). I was thinking about using an AC motor, but those are expensive with a pot to control the speed?

What would you guys suggest is the best motor type I should use? AC or DC motor?
Also, how would I control the speed? Would a pot be the best way to go or am I going to need to create a PWM signal with an arduino or something similar?

 

[Imozeb]

Could I use an arduino to power a small DC motor?

 

[sophiecentaur]

Hi and welcome.
I imagine you would need a bigger motor than the arduino will supply on its own. Look at adverts / specs for commercial treadmills and see what sort of Power they use. I guess you are looking at a fractional horsepower brush (AC/DC) motor, such as you get in washing machines. The control board on a washing machine is a pretty beefy item and will provide speed control if you give it the right signals. Once you have decided on the power of your motor, the electronics can be chosen to fit.

 

[Imozeb]

Thanks.

I know that I could use an arduino with a transistor to control the on/off of a much larger voltage source; however, is there any way that I could build in a variable speed (Like a pot) that is controlled by the arduino to control AC power from an outlet?

My circuit would be:
Arduino is hooked up to my computer to do data processesing.
Arduino is hooked up somehow via a transistor circuit to control a high resistance pot that controls the resistance across the outlet to AC motor circuit.

Is this possible? I don't know if pots can vary the voltage like I want? Any master insight would be appreciated.

 

[sophiecentaur]

You would use something like PWM. But, as I wrote earlier, the important thing is the Power of the motor. That will dictate the technology you use for the speed control. (Absolutely anything but a transistor used as a variable resistor - that would be soooooo 1960s.)

 

[billy_joule]

I wouldn't bother with arduino (expensive) or AC (dangerous) for something so simple and low powered.
I'd build the treadmill, estimate torque required at the required speed by hanging weights off pulleys. Possibly while something of lizard weight was sitting on the treadmill to simulate the added belt friction. (A toy car perhaps, with a string to keep it on the treadmill).
If you measure the fall speed of the weight you can calculate required power via power = torque * rotational speed (P=Tω)
I'd buy a 9-12 volt DC motor of the appropriate power output - note the rotational speed - this will affect how much reduction gearing you require.
The only work done is on friction so if you have a nicely tensioned belt (PTFE sheet will work well under the belt) and well greased bushes, nicely meshing gears etc the power requirements should be low.
I'd power it off something like this (As I have a couple laying around, think they were $15 each) so the speed can be adjusted.

http://www.dicksmith.co.nz/media/catalog/product/cache/3/image/275x/9df78eab33525d08d6e5fb8d27136e95/m/9/m9_dsnz_m9927_v0_4105.jpg

I'd test it on the lizard and if I couldn't get the required speed by adjusting the voltage I'd build a cheap PWM to allow finer speed control.
If you don't feel confident sourcing the parts for a PWM you could get a kit for under $10. Here's one:

http://www.ebay.com/itm/DC-Motor-Sp...330?pt=LH_DefaultDomain_0&hash=item233d9ae772

It sounds like a cool project, good luck.

 

[sophiecentaur]

I re-read the OP and got the bit about the lizard and the relatively low power.
Clearly, you won't be running this thing for as long as a Gym Treadmill so you might consider a Scalextric style speed controller and motor. That's a brute force method but it's already been done for you, which is a advantage if you're more into lizard activities than electronics; all you would need would be to take a scalextric motor and mount it with the appropriate belt drive and pulleys. A suitable DC PSU would be easy to get hold of.